[m-rev.] for review: complete switches on 8- and 16-bit fixed size integers

[Julien Fischer]

For review by anyone.

(I've omitted the body of the new tests cases since it's rather long and
not interesting.)

------------------------

Complete switches on 8- and 16-bit fixed size integers.

compiler/type_util.m:
     Treat complete switches on 8- and 16-bit fixed sized integers as det.
     (We don't do the same for the other fixed size integer types, since having
     a complete switch on them is not practical anyway.)

tests/valid/Mmakefile:
tests/valid/compare_{int8,uint8}_switch.m:
     Add a test for complete switches on the 8-bit integer types.


diff --git a/compiler/type_util.m b/compiler/type_util.m
index be20946..952db8a 100644
--- a/compiler/type_util.m
+++ b/compiler/type_util.m
@@ -2,6 +2,7 @@
  % vim: ft=mercury ts=4 sw=4 et
  %-----------------------------------------------------------------------------%
  % Copyright (C) 1994-2012 The University of Melbourne.
+% Copyright (C) 2014-2018 The Mercury team.
  % This file may only be copied under the terms of the GNU General
  % Public License - see the file COPYING in the Mercury distribution.
  %-----------------------------------------------------------------------------%
@@ -226,13 +227,13 @@
  :- pred type_constructors(module_info::in, mer_type::in,
      list(constructor)::out) is semidet.

-    % Given a type on which it is possible to have a complete switch,
-    % return the number of alternatives. (It is possible to have a complete
-    % switch on any du type and on the builtin type character. It is not
-    % feasible to have a complete switch on the builtin types integer,
-    % float, and string. One cannot have a switch on an abstract type,
-    % and equivalence types will have been expanded out by the time
-    % we consider switches.)
+    % Given a type on which it is possible to have a complete switch, return
+    % the number of alternatives. (It is possible to have a complete switch on
+    % any du type, on the builtin type character and on the builtin fixed size
+    % integer types. It is not feasible to have a complete switch on the
+    % builtin types int, uint, float, and string. One cannot have a switch on
+    % an abstract type, and equivalence types will have been expanded out by
+    % the time we consider switches.)
      %
  :- pred switch_type_num_functors(module_info::in, mer_type::in, int::out)
      is semidet.
@@ -1268,12 +1269,28 @@ substitute_type_args_ctor_args(Subst, [Arg0 | Args0], [Arg | Args]) :-

  switch_type_num_functors(ModuleInfo, Type, NumFunctors) :-
      type_to_ctor(Type, TypeCtor),
-    ( if TypeCtor = type_ctor(unqualified("character"), 0) then
+    ( if
+        TypeCtor = type_ctor(unqualified("character"), 0)
+    then
          module_info_get_globals(ModuleInfo, Globals),
          globals.get_target(Globals, Target),
          target_char_range(Target, MinChar, MaxChar),
          NumFunctors = MaxChar - MinChar + 1
-    else if type_ctor_is_tuple(TypeCtor) then
+    else if
+        % It's not worth bothering with the 32- and 64-bit integer types here
+        % -- a complete switch on any of those types would be so large that it
+        % would overwhelm the compiler anyway.
+        TypeCtor = type_ctor(unqualified(IntType), 0),
+        ( IntType = "int8", NumFunctors0 = 256
+        ; IntType = "uint8", NumFunctors0 = 256
+        ; IntType = "int16", NumFunctors0 = 65536
+        ; IntType = "uint16", NumFunctors0 = 65536
+        )
+    then
+        NumFunctors = NumFunctors0
+    else if
+        type_ctor_is_tuple(TypeCtor)
+    then
          NumFunctors = 1
      else
          module_info_get_type_table(ModuleInfo, TypeTable),
diff --git a/tests/valid/Mmakefile b/tests/valid/Mmakefile
index 0b992fa..3c3d1ae 100644
--- a/tests/valid/Mmakefile
+++ b/tests/valid/Mmakefile
@@ -89,6 +89,8 @@ OTHER_PROGS = \
  	builtin_false \
  	call_failure \
  	common_struct_bug \
+	complete_int8_switch \
+	complete_uint8_switch \
  	compl_unify_bug \
  	complicated_unify \
  	constr_inst_syntax \
diff --git a/tests/valid/complete_int8_switch.m b/tests/valid/complete_int8_switch.m
index e69de29..2e0f439 100644
--- a/tests/valid/complete_int8_switch.m
+++ b/tests/valid/complete_int8_switch.m
diff --git a/tests/valid/complete_uint8_switch.m b/tests/valid/complete_uint8_switch.m
index e69de29..7ccbf17 100644
--- a/tests/valid/complete_uint8_switch.m
+++ b/tests/valid/complete_uint8_switch.m